Anti-skid hydraulic brake system



Jan. 20, 1959 P. T. KEIM ET AL ANTI-SKID HYDRAULIC BRAKE' SYSTEM Filed May '7, '1954- xz imam United States ANTI-sion HYDRAULIC `BRAKE SYSTEM Paul T. Keim, Vandalia,iand Robert C. Treseder, Dayton,

Ohio, assignors to General Motors Corporation, Detroit, Mich., a corporation of Delaware Application May 7, `1954, Serial No. 428,224

Claims. (Cl. 18S-181) This invention pertains to hydraulic brake systems, and particularly to means for preventing the locking of any one wheel on a motor vehicle equipped with hydraulically operated brakes.

The hazards of driving a motor vehicle on slippery road surfaces are well recognized. Numerous vehicle accidents can be attributed to the skidding `of motor vehicles on slippery roads due to the locking of a vehicle wheel when the brakes are applied. This invention relates to simple and economical means for preventing the locking of any one Wheel of a motor vehicle equipped with hydraulically operated brakes. Accordingly, among our objects are the provisions of means for preventing the locking of any one Wheel of a motor vehicle having hydraulically actuated brakes due to braking of the vehicle; the4 further provision of means for automatically rendering the hydraulic braking system of a vehicle inoperative if any one wheel should become locked during braking, so as t0 freeall wheels for rotation; and the still further provision of means for automatically rendering the hydraulic braking system operative after the locked Wheel, or wheels, have been released.

The aforementioned and other objects are accomplished in the present invention by incorporating a fluid v pressure system responsive to the operative condition of the vehicle wheels for controlling the operability of the hydraulic braking system of the motor vehicle. Specilically, the mechanism of this invention includes a fixed displacement pump driven by each wheel. The pumps for the Wheels on each side of the vehicle are connected in parallel, and the flows produced by the pumps on each side of the vehicle are thereafter combined. The combined output ows of the pumps on one vehicle side traverses an actuating chamber for one side of a servo actuated,`reciprocable valve, or ow rate comparator, and the combined output flows of the pumps on the other vehicle side traverses an actuating chamber for the other surface of the comparator valve. The system `also includes a fixeddisplacement, engine driven pump which supplies pressure uid to a supply port of the comparator valve.

The ow comparator is a two-way valve having a pair of control ports connected by a conduit to a brake unloading actuator. The ow comparator is arranged to be maintained in the neutral position at all times except when `any one vehicle wheel is locked, at which time, the unequal flows produced by the wheel driven pumps will actuate the comparator valve. It should be noted that in the embodiment disclosed, locking of any one vehicle wheel, both wheels on the same side of the vehicle, and locking of three wheels will cause operation of the comparator valve, but'the simultaneous locking of two vehicle wheels on opposite sides of the vehicle and the simultaneous locking of all vehicle wheels of a four-wheel vehicle will not effect operation of the comparator valve. The brake unloading actuator includes a v cylinder having disposed therein a spring biased piston capable-o Quid pressure actuation iu one direction. V"flu". itiitt'f l Patented Jan. 20, 1959 piston has a rod operatively connected with a brake unloading piston disposed in a brake unloading cylinder. Accordingly, when the comparator valve is actuated so as to direct flow from the engine driven pump to the actuator cylinder, the brake unloading piston will be displaced so as to increase the volume of the brake unloading cylinder. As the brake unloading cylinder is connected by a conduit to the master cylinderof the hydraulic braking system, the hydraulic brake lines, or conduits leading to the brake cylinders, associated with each wheel will have the pressure therein relieved so as to free all wheels for rotation. Thus, when the volume of the unloading cylinder is increased while the brakes are being applied, the pressure created in the hydraulic brake lines by the master cylinder will be relieved so as to free `the locked vehicle wheel, `or wheelsQfor rotation. However, as soon as all wheels are again free for rotation, the comparator valve will be actuated so as to interrupt the application of pressure liuid to the actuator whereby the spring will reposition the actuator piston. 1n this manner, the unloading piston will restore pressure in the hydraulic brake lines so as to render the hydraulic braking system operative.

Further objects and advantages of the present invention will be apparent trom the rollowing description, reference being had to tne accompanying drawing wherein a preferred embodiment of the present invention is clearly shown. t

'the drawing represents a schematic diagram of the anti-skid brake system or' the present invention.

With particular reference to tne drawing, a four-Wheel motor vehicle is disclosed, the wheels being indicated by numerals 1li, 12, 14 and 16.A 'Each wheel is operatively connected to and drives a iixed displacement pump, the pumps being indicated by numerals 20, 22, 24 and 26. The intake vsides of pumps 20 and 26 are connected by conduits 30 and 36 to a conduit 23 which. connects with a sump or supply tank 18, while the inlets of pumps 22 and 24 are connected with conduits 32and `34 with a conduit 3:8,` which, likewise, connects with the sump 18. The outlet sides of' pumps 20, 22, 24 and 26 are connected to conduits 4i), 42, 44 and 46, respectively. Thus,

it may be seen that the pumps 20 and 22 on one side of the motor vehicle are connected in parallel, while the pumps 24 and 26 on the other side of the vehicle are, likewise, connected in parallel. The output of pumps 29 and 22, which flows through conduits 40 and 42, respectively, is co-mbined and flows through a conduit 4S, and this combined how traverses an actuating chamber 62 and, thence, flows through conduit Sti "to the'sump 18. The conduit Sti is connected to the chamber 62'through a restricted orifice so as to maintain a pressure head in chamber 62 during operation of pumps`20 and 22. Similarly, the iiows from pumps 24 and 26 are combined and flow through conduit 52, theV combined flows traversing an actuating chamber 64 and, thence, flowing through conduit 54 to the sump 18. The conduit 54 is connected lto the chamber 64 through a restricted orifice so as to maintain a pressure head in the chamber 64 during operation of pumps 24 and 26.

The vehicle is shown equipped with an hydraulically actuated brake system including a pivotally mounted, manually operable brake pedal 100, which is operatively connected to the rod 102 of a piston 104 disposed in a master cylinder idd. The master cylinder has communication with a reservoir w8 containingbrake fluid and also has communication with a conduit liti, which connects with brake lines 129, 122, 12.4 and 126,that connect with the wheelI carried brake cylinders 139,132, 134 and 136, respectively. The hydraulic braking system, per se, is conventionalin that upon operati-en of the pedal lili?,

the `brake lines are pressurized" as are the wheel cylinders actuator.

asados? so as to actuate individual wheel brakes, which operate Yto restrain rotation of the wheels.

The master cylinder 106 is also connected by a conduit 90 Ito a brake unloading cylinder'92, which has disposed therein a brake unloading piston 94. The brake unloading .piston94 is connected by a rod ,96 to an actuator piston .82 ydisposed in an-actuator ycylinder 84. The actuator piston 82 ris capable of uid pressure by actuation to the left, as viewed'in the drawing, and is normally urged to the position shown by means of a compression spring 86. The rod end chamber of cylinder 92, as well as the head end chamber of cylinder 84 are connected to drain conduit 53. The rod end chamber 8S of the cylinder S4 is connected bya conduit 76 to ports 72, 74 and 76 of a ow comparator which is designated generally by the nu meral 150.

The flow comparator vincludes a valve casing 6@ having disposed therein a reciprocable plunger 66, which is normally centered in the neutral position by oppositely acting springs@ and 73. The plunger 66 is formed with axiallyspaced lands 152, 154 and 156. `In the neutral position of plunger 66, as shown in the drawing, the lands 152 and 154 .closeiports 72 and 74.

The valve casing 60 also includes a supply port 158 and a drain port 160,V the drain port 160 being connected to conduit 50. The supply port 158 is connected to a conduit 162 to the output side of a fixed displacement engine driven pump 164, the inlet-side of which is connected by a conduit 166 to the conduits 36 and 2g and, thence, to the'sump .18.

During operation of the motor vehicle, the engine driven fixed displacement pump 164 will draw fluid from sump TLS, increase the pressure thereof and discharge the same through conduit 162. Similarly, during movement of the'kvehicle, each of thetixed displacement wheel driven pumps 29, 22, 24 and 26 will draw duid from the sump 18, increase the pressure thereof, and discharge the same into lconduits 40, 42, t4 and 46, respectively. The combinedtiows from pumps v26 and 22 will iiow through conduit 48 and traverse actuating chamber 62, while the combined flows from pumps 24 and 26 will flow through conduit 52 and traverse actuating chamber 64. `inasmuchas the wheel driven pumps are identical, the ows under pressure traversing the oppositely acting actuating chambers 62 and 64 will, likewise, be equal and the valve plunger 66 will remain .in the neutral position. Similarly, when the operator applies the brakes Vby actuating pedal ldd, and all of the wheels are thereby gradually restrained against rotation, the ows under pressure traversing the oppositely acting, actuating chambers 62 and 6d will be equal and the valve plunger 66 will remain inl the neutral position. However, if upon application of the brakes, wheel 1d should become locked while wheels 12, 14 and16 are gradually decelerated by their respective brakes, actuating chamber 64 will have a greater flow under pressure therethroughrthan will actuating chamber 62, and in .this manner, the plunger 66 will be servo actuated and moved to the right, as viewed in the drawing. When the plunger 66 moves to the right, the supply port S will connect with port 7d, land i543 at this time blocking communication between drain ports 76. and 160, so that iiuid under pressure from the conduit 162 will be applied through conduit '70 to the chamber 8S of the In this manner, the actuator piston 82 will be moved to the left and concurrently therewith the brake unloading piston 9d will be moved to the left, as viewed in the drawing. In this manner, the pressure created by the master piston in the brake lines will be relieved so as to free all wheels on the vehicle for rotation. Thus, thel tendency of the vehicle to skid will be prevented. it should be noted Vthat the yanti-slddding system will render Vthe braking system inoperative when any one vehicle wheel becomes locked, or `an Iodd number of wheels be vcome locked. 'InadditioinY the-anti-skid system will render when two wheels on the same side of the vehicle become locked. However, it is apparent that the anti-skid system will not render the hydraulically actuated brake system inoperative when two wheels on opposite sides of the vehicle become locked or when all of the vehicle wheels become locked.

After operation of the flow comparator valve so as to render the hydraulically actuating braking system inoperative, thereby freeing all wheels for rotation, the hydraulic operatingbraking system will again be rendered operative inasmuch Vas all of the Wheel driven xed displacement pumps will again be operative. Thus, equal Hows will traverse the oppositely acting, actuating chambers 62 and 64, thereby permitting the centering springs 63 and 78 to reposition the'plunger 66 in the neutral position, as shown in the drawing, thus connecting the actuator cylinder to drain through ports 76, and conduit 56.

While theembodiment of the present invention as herein disclosed, constitutes a preferred form, it is to be understood that other forms might be adopted.

What is claimed is as follows:

l. Brake mechanism for a motor vehicle having a plurality of wheels, including in combination, a fluid pressure operated brake for each Wheel, a braking system for applying fluid under pressure concurrently to each wheel brake, a fluid pressure system includinga,iixeddisplacement pump driven by each wheel, means connecting the pumps on each side of said vehicle in parallel, means for relieving the pressure in said braking system for rendering said braking lsystern inoperative, and means operatively connected-to said pressure relieving means and responsive to the absence of flow from any one of said fixed displacement pumps as caused -by locking of any one vehicle wheel during kbraking-for positively actuating said pressure relieving .means so as to render said braking system inoperative; A

2. Brake mechanism for a motor vehicle having a plurality of wheels, including 4in combination, a uid pressure operated 'brake for each wheel, a braking systern for applying fluid under pressure concurrently `to each wheel brake, means for relieving the pressure in said braking system so as to render said system inoperative, said pressure relieving means including a brake positively operate saidbrake unloading'piston including a fixed displacement pump operatively connected to and driven by each wheel, means connecting the output of the pumps on each side of the vehicle in parallel yand means for comparing the flows produced by the pumps on each side of the vehicle and responsive to unequal iiows produced thereby ,for actuating said pressure -relieving means whereby `the locking of any one vehicle wheel will result in operation of vsaid brake unloading piston to render the braking system inoperative.

3. The combination set ,forth in claim 2 wherein the meansvresponsive to unequal `flows produced `by said wheel driven displacement pumps comprises a normally spring centered flow comparator valve having oppositely acting, .actuating chambers which are .subjected `to the combined flows produced by the pumps on oppositersides of said vehicle. Y

4. Brake mechanism for a vehicle having a plurality of Wheels, including incombination, a uid pressure operated-brake for each wheel, 'a braking system vfor applying duid under pressure concurrently to each wheel brake, apurnp driven by each-wheel, means connecting the outlet side ofthepurnps kon each `sideV of the vehicle in parallel, rneans for comparing the output "flows produced by the pumps on each side ofthe vehicle, Vfluid pressure actuated brake'unloadirlg means for relieving the pressure iii-said v.braking 'system jto render A.said `braking 5 system inoperative, a source of uid pressure for actuating said brake unloading means and a valve interconnecting said source of uid pressure and said brake unloading means and actuated by said flow comparing means for displacing said valve in response to unequal output flows produced by said pumps.

5. The combination set forth in claim 4 wherein said flow comparing means comprises a normally spring centered servo mechanism having opposed chambers subjected to the combined output flows of the pumps on opposite sides of said vehicle, and wherein said brake unloading means comprises a cylinder having disposed therein a piston, said piston beingV spring biased in one direction and capable of uid pressure actuation in the other direction.

References Cited in the le of this patent UNITED STATES PATENTS Wildin et al. May 4, Whitaker Ian. 26, Hallot 1- Feb. 8, Aikman c- Oct. 11, Piron Sept. 28, Thomas et al. June'24, Curl et al. July 3, Carlson et al. Aug. 21,

FOREIGN PATENTS France May 18,

Great Britain May 15, 

